Agriculture Reference
In-Depth Information
of 'Williams' Bon Chretien' pear. There is ample evidence of this in apple
also; for example, Jonkers (
% of terminal buds
initiate flowers in successive years. This results in a strong negative relationship
between fruits per blossom cluster, on whole trees, in one season and number
of blossom clusters in the following year (Landsberg,
) reported that only
-
).
The presence of seeded fruits for only
-
days after their pollination is
enough to prevent about
% of apple spurs from flowering in the following
year, although flowering is further reduced if the fruits are left on for
days
from pollination (Chan and Cain,
). An effect of fruits late in the season
was also shown by Williams
et al.
(
), who harvested 'Bramley's Seedling'
apple at four different dates, from
October. Fruit weight almost
doubled between the first and last pickings. The number of primary blossom
clusters in the following year was more than
August to
% higher on the trees harvested
on
October,
and the number of secondary blossoms several times as high. In 'Williams' Bon
Chretien' pear Huet (
August and
September than on those harvested on
and
) found the greatest adverse effects of seeded fruits
on flower bud development to be between
and
days after full bloom
when the fruitlets were of about
mm diameter.
Seedless fruits do not have the same adverse effect as seeded fruits. Chan and
Cain (
) hand-pollinated half of a tree of the parthenocarpic apple cultivar
'Spencer Seedless' and adjusted the fruit load so that it did not differ between
the seeded and seedless side of the tree. In the following year there was no
blossoming on the previously seeded side of the tree, but profuse blossoming
on the side where the fruits had been seedless. Similarly in 'Williams'' pear a
heavy crop of seedless fruits was followed by heavy flowering, whereas this was
totally inhibited by an equivalent crop of seeded fruits (Table
). In Chan
and Cain's study there was no difference in inhibition of flowering by different
numbers of seeds and the effect of seed number, as contrasted with the effects
of presence or absence, was small even in the third year.
The inhibitory effect of fruits on flower bud initiation is associated with
a slowing of bud growth from a plastochron of
.
days between successive
nodes to one of
days (Fulford,
c). It is accompanied by poorer vas-
cular development. Izadyar (
) found that in spurs with fruits there was
greater differentiation of vascular bundles towards the fruit pedicels than to-
wards the vegetative buds. These buds, which would normally be 'off', i.e.
non-flowering, in the following year were not connected to the spur vascu-
lar bundles. In contrast the potentially 'on', i.e. potentially flowering, buds
on spurs without fruits were connected with the vascular bundles of the
spurs at an early stage. The 'off' buds may therefore suffer relative nutrient
deficiency.
The lack of inhibiting effect of seedless fruits and the effects of the position
of seeded fruits on their inhibitory influence led to the view that seed-produced
